This invention relates to a telephone subset line switch, sometimes known as a `Line Interface Circuit`, which incorporates an electronic hook switch, usually in integrated circuit form.
Line switches of the aforementioned type are known and described in detail in, for example, the specification of Austrailian Patent Application No. 21,775/83. This specification describes a solid state switch for use as a hook-switch, comprising a field effect transistor whose gate/source potential is controlled by a bipolar transistor. Such a solid state hookswitch has an advantage over conventional mechanical hook-switches when "on hook dialling" is required, in that, expensive mechanically interlocked switches can be avoided.
The specification of Australian Patent Application No. 57,138/86 describes in detail a circuit arrangement in which the outpulsing transistor switch of a telephone subset's dialling circuit is utilized for generating a timed loop break recall signal. This known circuit arrangement has on the one hand, the advantage of obtaining a significant reduction of components by the characteristic utilization of the outpulsing transistor switch. But on the other hand, a conventional mechanical hook-switch is incorporated in the subset's circuit.